Interposer assembly

ABSTRACT

An interposer assembly includes a dielectric plate having a plurality of contact passages extending through the plate with a contact in each passage. Each contact includes a pair of laterally spaced contact points at the top and bottom of the plate. Sandwiching of the interposer assembly between two substrates brings the contact points on each spring arm into engagement with a pad, elastically bends the contacts and forms redundant high pressure wiped electrical connections between the contact points and pads.

This application is a division of U.S. application Ser. No. 09/897,332filed Jul. 2, 2001 now U.S. Pat. No. 6,730,134.

FIELD OF THE INVENTION

The invention relates to interposer assemblies of the type which aresandwiched between substrates to form electrical connections betweenopposed pads on the substrates, and to cantilever contacts for formingelectrical connections with contact pads.

BACKGROUND OF THE INVENTION

Interposer assemblies typically include plastic plates with throughpassages and contacts in the passages for forming electrical connectionsbetween opposed contact pads.

Interposer assemblies form electrical connections between contact padsarranged in a very close proximity to each other. The pads may bearranged on a one millimeter center-to-center grid. Each assembly mayinclude as many as 961 contacts with four interposer assemblies mountedin a single frame with a total of 3,844 contacts in the frame. Thecontacts must establish reliable electrical connections with the padswhen the assemblies are sandwiched together between circuit members.Failure of a single contact to make a reliable connection renders theentire frame useless.

Contacts in interposer assemblies include contact surfaces whichmechanically engage the contact pads and form electrical connectionswith the contact pads. Conventional interposer assemblies have singlesurface contacts which engage each pad to form a single electricalconnection with each pad. The contact may wipe along the pad to improvethe quality of the electrical connection. Impurities, oxides orcontaminants on either the contact surface or the pad can impair thesingle surface electrical connections with the pads. Contacts used ininterposer assemblies are typically symmetrical about the center of theinsulating plate, each including a separate spring which biases a singlecontact surface against a pad.

Accordingly, there is a need for an improved interposer assembly inwhich each contact makes redundant contacts with each pad so that whenthe assembly is sandwiched between overlying and underlying substrateseach contact establishes two reliable electrical connections with eachpad. The connections should have small contact areas to increase thecontact pressure between the contact and the pad. Wiped high contactpressure redundant connections would provide reliable interposerassembly electrical connections. There is also a need for a method ofmaking a contact with spaced contact points from strip stock, which maybe very thin and difficult to form.

Further, there is need for a spring contact having spaced contact pointsfor engaging a contact pad and forming redundant wiped high pressureredundant electrical connections between the contact and the pad.

SUMMARY OF THE INVENTION

The invention is an improved interposer assembly including contactsmounted in passages extending through an insulating plate s with eachcontact having two contact points on each end of the contact. When theinterposer assembly is sandwiched between overlying and underlyingsubstrates the pairs of contact points are brought into wiped pressureengagement with overlying and underlying pads and forms redundantelectrical connections with the pads.

The contact points are formed on rounded edge corners of the contactsand have small contact areas, resulting in high contact pressure andreliable electrical connections despite debris, oxides and surfacecontaminants on the contacts and pads.

Each contact includes two tapered spring arms joined to a centralportion. A pair of contact points is formed on the outer end of eachspring arm. The points project above and below the plate. The arms areindependently deflected during compression of the contact by overlyingand underlying substrates. The spring arms may include retention legsextending outwardly from the contact points for engagement with adjacentcam surfaces. Compression of the contacts moves the ends of the legsalong the cam surface to further stress the spring and increase contactforce.

Additionally, the invention relates to a contact having a beam with amounting end and a contact end carrying a pair of laterally spacedcontact points. Movement of a pad against the contact points stressesthe beam and moves the contact points laterally along the pad to formwiped high pressure electrical connections between the contact and thepad. The contact points are rounded edge corners and have a very smallcontact area in order to increase contact pressure and form redundantwiped high pressure electrical connections between the contact and thepad. The contact points are preferably located on opposite sides of thespring arm and stabilize the contact against twisting.

Other objects and features of the invention will become apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawings illustrating the invention, of which there arefive sheets of drawings and two embodiments.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view, broken away, of an interposer assembly accordingto the invention;

FIG. 1A is an isometric view of a contact used in the interposerassembly;

FIG. 2 is a top view of a substrate with pads for forming electricalconnections with the contacts in the interposer assembly;

FIG. 3 is a sectional view taken along line 3—3 of FIG. 1;

FIG. 4 is a view like FIG. 3 showing the interposer assembly sandwichedbetween top and bottom substrates;

FIG. 5 is an enlarged view of portion of FIG. 4 showing an alternativeconstruction;

FIG. 6 is a view like FIG. 4 showing the substrates engaging theinterposer assembly;

FIG. 7 is a view like FIG. 2 showing wipe traces on the contact pads ofthe substrate;

FIG. 8 is a partially broken away view taken along line 8—8 of FIG. 6;

FIG. 9 is a contact preform;

FIG. 10 is an enlarged view of a portion of the preform of FIG. 9showing a pair of wings;

FIG. 11 is a sectional view taken along line 11—11 of FIG. 9 showing thewings bent upwardly;

FIG. 12 is a sectional view showing tooling used for punch forming thepreform from strip stock; and

FIGS. 13 and 14 are sectional views showing a cantilever contact relatedto the interposer contact.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disclosure relates to the interposer assembly of U.S. Pat. No.6,176,707, the disclosure of which is incorporated herein by referencein its entirety.

The disclosure also relates to the interposer assembly of Neidich, etal. U.S. Pat. No. 6,290,507 the disclosure of which is incorporatedherein by reference, in its entirety.

The first embodiment interposer assembly 10 includes a flat dielectricplate 12 preferably molded from thermoplastic resin and having aplurality of contact passages 14 extending through the thickness of theplate from plate top 16 to plate bottom 18. A contact 20 is held in eachpassage 14. The height of plate 12 may be as little as 0.048 inches.

Passages 14 are elongate in transverse cross section. Each passageincludes a wide end 22, an opposed narrow end 24, a uniform widthportion 26 adjacent the wide end 22 and a tapered, reduced width portion28 adjacent the narrow end. The uniform width portion 26 has opposedparallel walls extending between the top and bottom of the plate and thereduced width portion has inwardly tapered walls extending from portion26 to narrow end 24.

As illustrated in FIG. 3, a shallow contact-retention projection 30 isformed in each narrow passage end 24. The projection is defined by flatupper and lower cam surfaces 32 and 34 extending from projection tip 36to the top and bottom of plate 12 respectively. The tip is locatedequidistant between the top and bottom of the plate. Both cam surfacesslope away from the tip at a shallow angle of about 12 degrees from thevertical. Flat end wall 38 at wide passage end 22 extendsperpendicularly between the top and bottom of plate 12.

FIG. 5 illustrates a modified interposer assembly plate 12 a similar toplate 12 and having a top cam surface 32 a and bottom cam surface (notillustrated) which end a short distance 98 inwardly from the plate topside 16 a and bottom side (not illustrated). The cam surfaces and short,straight end wall surfaces 98 at the top and bottom sides of the plateextend across the narrow end 24 a of contact passage 14 a.

Plates 12 and 12 a are molded from thermoplastic resin using moldsupporting core pins forming passages 14 and 14 a. The toolingsupporting the core pins normally extends a very short distance into themold cavity to prevent the cam surfaces from extending to the top andbottom of the plate. Each straight surface 98 has a vertical extent ofabout 0.005 inches so that, in practice, the cam surfaces are recessedfrom the top and bottom of the plate only a very small distance. Thisrecess distance does not effect the operation of the interposerassembly.

Contact 20 is formed from thin uniform thickness metal strip stock,which may be a beryllium copper, and is preferably plated with aconductive metal, which may be gold or a gold alloy, to reduce contactresistance and prevent oxidation. Contacts 20 may be made from stripstock having a thickness of 0.0017 inches. This thin stock is difficultto shape accurately.

Contacts 20 include a flat central portion or spine 40, like upper andlower curved and tapered spring arms or beams 42. Arms 42 extend inopposite directions from spine 40. Contact noses 44 are located at theupper and lower ends of the spring arms. Short, straight and taperedretention legs 46 extending outwardly from the noses and toward eachother to rounded ends 48. When contacts 20 are unstressed the noses 44are spaced apart a distance of 0.060 inches, greater than the thicknessof plate 12. Spring arms 42 are bent laterally away from central spine40 in the same direction so that noses 44 are located between the spineand retention leg ends 48. Arms 42 have a maximum width adjacent spine40. The width of each arm decreases from the spine to nose 44. Contacts20 are symmetrical to either side of spine 40.

Each spring arm 42 includes a pair of contact points 50 adjacent nose44. The contact points are spaced apart on opposite sides of the springarm a short distance inwardly from the nose and project above thesurface of the arm. As shown in FIG. 1, the contact points also arelocated outwardly from the arms to increase the width of the contactadjacent the nose.

FIG. 9 illustrates preform 52 which is stamped from uniform thicknessstrip stock and shaped to form contact 20. The preform includes acentral portion 54 which forms spine 40 and two, like arm or beamsections 56 extending to either side of the central portion which formarms 42 and legs 46. The widths of the arm sections decrease from amaximum at the central portion to minimums at ends 58. Roundedprojections or wings 60 extend outwardly from the sides of the armsections between the central portion 54 and ends 58.

FIG. 12 illustrates tooling used to stamp preform 52 from thin stripstock 62. The strip stock is positioned on anvil 64 with an overlyingpressure plate 66 clamping the strip stock to the anvil. Cutters 68,located to either side of the plate and anvil and above strip stock 62,are moved down past the anvil to cut or shear away outer portions 70 ofthe strip stock from the portion 72 held between the anvil and pressureplate. Sharing forms sheared edges 74 on held portion 72 with roundedupper corners 76 and sharp, drag lower corners 78. In the drawings, thesize of corners 76 and 78 is exaggerated for clarity.

Stamped preform 52 includes cut edges 74 extending along the sides ofboth arm sections 56 and around the wings or projections 60 on the armsections. Rounded edge corners 76 are located on one side of the preformand drag corners 78 are located on the other side of the preform.

Contact 20 is formed from preform 52 by bending the preform about axesparallel to the plane of the preform to form curved spring arms 42,noses 44, legs 46 and curved ends 48 at the ends of legs 46. The preformis bent to locate rounded edge corners 76 on the outside of the contactand drag corners 78 on the inside of the contact.

Additionally, during bending of the preform to form the contact, or asan independent step, both projections or wings 60 are bent upwardlyrelative to the arm sections, around bend lines 80 shown in FIG. 10, toform contact points 50 extending above the spring arms 42 adjacent tonoses 44. FIG. 7 illustrates the bent up wings with rounded corners 76located above the arm section 56 and with the drag corners 78 locatedoutwardly and below the rounded corners.

Contact preform 52 may have a thickness of 0.0017 inches. Metal of thisthickness is very hard to handle and shape reliably. The small diameter,rounded corners on the contact points are formed during shearing of thepreform from strip stock material without the necessity of physicallybending the strip stock. The rounded corners are very small having atransverse radius of curvature of about 0.0006 inches to 0.0010depending on tool clearance and wear. It would be very difficult to formthese small rounded corners by mechanically shaping the preform. Theradius of curvature along the length of the corners is about 0.012inches.

After bending of preform 52 to form contact 20 as described, the contactis preferably plated with a conductive metal which may be gold or a goldalloy to form a plating 82 surrounding the contact.

Formed and plated contacts 20 are inserted into contact passages 14 inplate 12 by positioning each contact to one side of a passage with acontact nose located adjacent the center of the passage, spring arms 42adjacent wide passage end 22 and retention legs 46 adjacent narrowpassage end 24. The contact is then moved into the passage to bringspine 40 into engagement with wall 38 and the lead retention leg 46 intoengagement with the adjacent cam surface 32 or 34. This engagementresults because the horizontal distance between the spine and curvedends 48 of legs 46 is greater than the minimum spacing between tip 36and wall 38. Continued movement of the contact into the passageelastically stresses the contact to move the leg inwardly and permitmovement the leg past the projection to the inserted position shown inFIG. 3. After the leg passes the projection tip the contact returns tothe shape shown in FIG. 3. In this position the contact 20 is unstressedand loose in passage 14. Projection 30 extends between the ends of theretention legs 46 to prevent dislodgement of the loose contact from thepassage.

FIG. 3 shows loose contact 20 with the retention legs away from theprojection. In practice, gravity will shift the contact down in thepassage so that the upper leg 46 rests on upper top cam surface 32. Withcontact 20 in passage 14 as illustrated, the upper and lower contactnoses 44 are located at the top and bottom of the contact. The contactpoints 50 are also located at the top and bottom of the contact. Noses44 extend across the width of the contact. Projections 50 are located onthe opposed sides of the contact.

In one interposer assembly 10 having a plate 12 with a thickness of0.048 inches and contact 20 formed from uniform thickness strip stockhaving a thickness of 0.0017 inches the height of the unstressedcontacts from nose to nose is 0.060 inches. When the contact ispositioned in a contact passage 14 as shown in FIG. 3 each contact nose44 projects a distance 0.006 inches above the top or bottom side of theplate. The contact points 50 are spaced apart across the width of thecontact 0.0115 inches.

Interposer assembly 10 is used to establish electrical connectionsbetween opposed contact pads 84 on substrates 86 located to either sideof the assembly. FIG. 2 illustrates the contact surface of a substrate86 with pads 84. FIG. 4 illustrates the interposer assembly 10 locatedbetween substrates 86 with the contact pads 84 lightly engaging thecontact noses 44 and contact points 50 on each end of contacts 20 inpassage 14 with contact 20 unstressed.

FIG. 6 illustrates interposer assembly 10 fully sandwiched betweensubstrates 86 with the contact pads 84 on the substrates engaging thetop and bottom plate surfaces and contact 20 collapsed into passage 14.During movement of the substrates onto the plate each contact nose iscollapsed 0.006 inches into the passage, the rounded ends of theretention legs 46 are brought into engagement with the upper and lowercam surfaces 32 and 34 and are moved inwardly along the surfaces to theposition shown in FIG. 3 adjacent tip 36. As the contact is collapsed,the retention legs 46 and the spring arms 42 are bent laterallyelastically to provide high contact pressure between the ends of thecontact and the pads 84 and to wipe the points along the pads. Thespring arms 42 and central portion or spine 40 form an elastic springsystem. In this position, contacts 20 are held in the passages by thesubstrates.

As contact 20 is collapsed into passage 14 the ends of arms 43 rotateand engagement between the outer ends of the arms and pads 84 movesalong the arms from noses 44 to the adjacent rounded corners 76 at thetops of the contact points 50. Compare FIGS. 4 and 6. The rounded edgecorners 76 at the tops of the contact points 50 wipe along pads 84 toform wipe traces 88 shown in FIG. 7. Each trace 88 extends from a pointof initial contact 90 between a point 50 and the pad to a final contactposition 92. The contact points move along traces 88 in a direction awayfrom passage wide end 22 and toward passage narrow end 24. Theresiliency of the stressed spring system biases the small area roundedcorners 76 of points 50 against the contact pads under high pressure asthe points are moved along traces 88. The contact pressure exerted bythe spring system is applied to the pads at the small four roundedcorners 76 of points 50, resulting in redundant high pressure electricalconnections between the points and pads. The contact pressures are highbecause the contact areas are low. High pressure wiped engagementbetween the points 50 and the pads breaks through debris, oxides orother surface contaminants on the points or on the pads. The roundedcorners slide along, but do not cut into the pads. The provision ofredundant contacts at each end of contacts 20 increases the reliabilityof electrical connection between contact 20 and pads 84 overconventional single area contacts.

During compression of contacts 20 into passages 14 the two contact arms44 are each bent away from wide passage end 22 independently of eachother with contact central portion or spine 40 held on end wall 22,although the contact may shift vertically a slight distance in thepassage to shift the spine up or down along wide end wall 22. Each arm42 is stressed essentially independently of the other arm 42 so that thecontact pressure at points 50 on one end of the contact is provided byelastic deformation of the adjacent spring arm 42 and retention leg 46,located to one side of the central portion. Thus, contact 20 includestwo like spring contacts each located to one side of the central portionand each including a curved tapered spring arm 42 and a taperedretention leg 46. The width of retention leg 46 decreases from nose 44to end 48 to permit ready deflection of the leg by the adjacent camsurface 32 or 34. Deflection of both the spring arm 42 and leg 46contribute to the spring force holding projections 50 against adjacentpad 84. Each of the independent, like spring contacts provides anelectrical connection between a contact pad and the spine 40 at thecenter of contact 20.

FIGS. 13 and 14 illustrate a cantilever spring contact 100 formed frombent uniform thickness strip stock, related to contact 20. The stripstock may have a desired thickness, which may be other than thethickness of contact 20. The contact 100 includes a mounting end 102 anda contact end 108. End 102 is mounted in substrate 104. A curved,tapered spring arm or beam 106 extends upwardly from the substrate andis bent laterally to one side of the mounting end 102. The mounting endis connected to a circuit element (not illustrated). Contact 100connects the circuit element to pad 114 on substrate 112.

Spring arm 106 may be identical to spring arm 42 in contact 20 and is abeam having a tapered width decreasing from a maximum width at mountingend 102 to a minimum width at contact end or end 108. A pair of contactpoints 110 having upwardly facing rounded edge corners are formed on theopposite sides of arm 106 at end 108. Arm 106, end 108 and contactpoints 110 may be identical to arm 42, nose 44 and contact points 50 ofcontact 20, previously described.

FIG. 13 illustrates substrate 112 located above substrate 104 andcarrying contact pad 114. Pad 114 engages end 108 and points 110 ofcontact 100 without stressing the contact.

Electrical connections are established between pad 114 and contact 100by reducing the distance between substrates 104 and 112 so that thespring arm 106 is elastically bent laterally and engagement between thecontact and the pad shifts from end 108 to the rounded corners of spacedcontact points 110, in the same way redundant contacts are establishedbetween the ends of the spring arms 42 in contact 20 and overlying andunderlying pads 84.

Elastic bending of the spring arm provides high contact pressureengagement between the points 110 and pad 114. The points are wipedalong the pad to form contact traces on the pad like traces 88 shown inFIG. 7. The wiped, redundant high pressure contacts between the contactand pad assure reliable low resistance electrical connections areestablished. The spaced apart contact points 110 support contact 100 onpad 114 to prevent twisting of the contact.

Contact 100 does not include a leg and curved end like retention leg 46and curved end 48 of contact 20. If desired, contact 130 may be providedwith a leg 116 having a curved end 118, like leg 46 and end 48, andsubstrate 104 may be provided with a cam surface 120, like top camsurface 32 in plate 2. Leg 116, end 118 and cam surface 120 are shown indashed lines in FIGS. 13 and 14. During collapse of spring 100 providedwith a leg 116 and end 118, end 118 engages cam surface 120, leg 116 iselastically deformed and increases the contact pressure between points102 and pad 114. The spring arm 110 with arm 116 and end 118 is deformedidentically to each half of contact 20 as the overlying and underlyingsubstrates 86 are moved together from the position of FIG. 4 to theposition of FIG. 6.

While I have illustrated and described a preferred embodiment of myinvention, it is understood that this is capable of modification, and Itherefore do not wish to be limited to the precise details set forth,but desire to avail myself of such changes and alterations as fallwithin the purview of the following claims.

1. An interposer assembly for forming redundant electrical connectionswith contact pads on substrates positioned above and below the assembly,said assembly comprising: a) an insulating plate having top and bottomsides and a plurality of passages extending through the thickness of theplate; and b) a plurality of metal contacts, each contact disposed inone of said passages, each contact including a first pair of spacedcontact points at the top side of the plate, a second pair of spacedcontact points at the bottom side of the plate, and a spring portionextending between said first pair of contact points and said second pairof contact points, said spring portion spacing said pairs of contactpoints apart a distance greater than the thickness of the plate when thespring portion is unstressed; each contact formed from uniform thicknessstrip stock having a first sheared edge, and at least one contact pointcomprises a shear-rounded corner of said edge located above the adjacentsurface of the metal contact; wherein the shear rounded corner forms anelectrical connection with a pad.
 2. The assembly as in claim 1 whereineach spring portion includes a central portion and a pair of beams, eachbeam located between the central portion and a pair of contact points,said beams elastically bendable into said passages.
 3. The assembly asin claim 2 wherein each contact point is bent to one side of a beam. 4.The assembly as in claim 3 wherein each contact point is rounded alongthe length of a beam.
 5. The assembly as in claim 4 wherein said stripstock has a thickness of about 0.0017 inches.
 6. The assembly as inclaim 4 wherein each contact point comprises a shear-rounded corner andsaid rounded corners have a radius of curvature of about 0.0006 to0.0010 inches.
 7. The assembly as in claim 4 wherein each contact issymmetrical to either side of the central portion.
 8. The assembly as inclaim 7 wherein the plate includes a projection extending into eachpassage, and each contact includes two retention portions located onopposite sides of a projection to retain the contact in the passage. 9.The assembly as in claim 1 wherein each contact includes a secondsheared edge, each contact point comprising a shear-rounded edge corner.10. The assembly as in claim 9 wherein each contact point comprises abent projection.
 11. An assembly adapted to be interposed between pairsof spaced metallic pads on substrates for forming electrical connectionsbetween the pads, said assembly comprising: a) a dielectric plate havinga top and a bottom, a plurality of spaced passages extending through thethickness of the plate from said top to said bottom thereof, saidpassages each including opposed interior walls, b) a projection in eachpassage, each projection extending outwardly from one of said interiorwalls toward an opposed interior wall and including a first surfacefacing said plate top and a second surface facing said plate bottom; c)a plurality of metal contacts, each contact disposed in one of saidpassages, each contact formed from thin sheet metal stock and includinga central portion, a pair of beams extending to either side of thecentral portion, a nose located on the end of each beam, and a retentionleg extending inwardly from each nose to an end located away from thecentral portion, said noses spaced apart a distance greater than thethickness of the plate when the contact is unstressed, each contactbeing located in a passage with the central portion adjacent an interiorwall away from the passage projection and the ends of the retention legslocated on opposite sides of the projection so that the projectionretains the contact in the passage; and d) each contact including a pairof laterally spaced contact points adjacent each contact nose; e)wherein upon compression of the contacts into the passages by opposedcontact pads, the beams are stressed, and the contact points on eachnose engage and wipe along a pad to form redundant wiped pressureconnections with the pad.
 12. The assembly as in claim 11 wherein saidbeams are curved.
 13. The assembly as in claim 12 wherein each contactpoint is located on an edge of a beam adjacent a nose.
 14. The assemblyas in claim 13 wherein each contact point is located at a corner of abeam edge.
 15. The assembly as in claim 11 wherein at least one contactpoint comprises a shear-wiped corner of a beam edge.
 16. The assembly asin claim 14 wherein said strip stock has a thickness of about 0.0017inch.
 17. The assembly as in claim 16 wherein said contact points arerounded and have a radius of curvature of about 0.006 inches.
 18. Theassembly as in claim 11 wherein each contact point comprises a portionof a contact bent to one side of the remainder of the contact.
 19. Theassembly as in claim 11 wherein said beams are tapered.
 20. The assemblyas in claim 11 wherein said retention legs are tapered.
 21. Aninterposer assembly comprising: a) an insulating plate having top andbottom sides and a plurality of passages extending through the thicknessof the plate; b) a plurality of elongate metal contacts, each contactformed from thin sheet metal having opposed longitudinally extendingsheared edges and including a pair of spaced apart curved noses, and aspring located between the noses, each nose extending across the widthof the contact between such sheared edges and including a shear-roundededge corner at each sheared edge, the edge corners facing outwardly ofthe assembly and located above the surface of the nose between said edgecorners, said edge corners being rounded along the length of thecontacts; and c) each contact located in a passage in the plate withsaid noses adjacent the top and bottom sides of the plate and spacedapart a distance greater than the thickness of the plate when thecontacts are unstressed; wherein the shear-rounded edge corners at eachhose form redundant electrical connections with contact pads onsubstrates overlying and underlying the plate.
 22. An interposerassembly as in claim 21 wherein said beams are curved.
 23. An interposerassembly as in claim 21 wherein each contact point is bent up from oneside of a contact end.